1. Technical Field
The present disclosure generally relates to a fixing member for toner fixing, a fixing device, and an image forming apparatus.
2. Related Art
An electrophotographic image forming apparatus, such as a copier or a printer, includes an image forming unit for forming a color image formed of toner of, for example, four colors (e.g., yellow, magenta, cyan, and black) on a recording medium and a fixing device for fixing the formed color image onto the recording medium. The fixing device includes a fixing member for fixing (hereinafter, simply referred to as “fixing member”) the color image onto the recording medium by heating and a pressing member forming a fixing nip with the fixing member. When the recording medium goes through the fixing nip, the fixing device fixes the color image formed of toner images of the four colors onto the recording medium with heat and pressure.
The fixing member is generally a roller shape or a belt shape. The fixing member has an elastic layer formed on a metal roller or a resin seamless belt and a heater in the metal roller or the resin seamless belt. The elastic layer includes a synthetic rubber such as silicone rubber. However, due to the elastic layer having small heat conductivity and large heat capacity, the warm up time may increase. To improve heat conductivity, it is proposed to include fillers in the elastic layer or a releasing layer.
In addition, the fixing member preferably has an elasticity that encompasses, melts, and mixes the toner of the four colors forming the color image when fixing the color image. Accordingly, the releasing layer formed of material with small elasticity such as a fluorine resin has a tendency to be thin.
JP-2005-292218-A discloses a roller for a fixing device with improved heat conductivity and shape stability of a silicone rubber by coating a fluorine resin on an outer circumference of an elastic layer formed of the silicone rubber including carbon fibers.
JP-2010-092008-A discloses a fixing belt having an elastic layer in which a blending ratio of fillers and carbon nanotubes (hereinafter referred to as CNT) is set within a predetermined range to obtain a desired elasticity, improved heat conductivity, and good mechanical fixing strength.
However, the above-described roller or belt uniformly disperses the carbon fibers or the CNTs within the whole elastic layer, which makes the elastic layer hard. When the elastic layer of above-described roller or belt is used with a recording medium having high surface unevenness, the elastic layer may not be able to follow the high surface unevenness, thus causing defective fixing.
JP-2010-170132-A discloses a fixing member including a base body, an elastic layer, and a releasing layer formed of a fluorine resin including fluorinated CNTs. The fixing member exhibits improved heat conductivity and improved mechanical strength. Accordingly, extended operation life is obtained. However, due to the releasing layer being hard, the difference in the degree of deformation between the elastic layer and the releasing layer is large. Accordingly, the releasing layer is susceptible to coming off, and to prevent the releasing layer from coming off, the elastic layer has a relatively small thickness to lower the degree of deformation. As a result, surface following capability in heating for fixing is insufficient.
A fixing member with an intermediate layer (or a primer layer) including fillers between an elastic layer and a releasing layer is also known. For example, JP-2010-066509-A discloses a fixing belt including a primer layer that contacts a surface layer having a fluorine resin. The primer layer includes a fluorine resin and inorganic fillers, and particle size distribution of the inorganic fillers is adjusted to a predetermined range. JP-2009-103882-A discloses a pressing roller including an adhesive layer for bonding an elastic layer and a releasing layer. Fillers of anisotropic property having high heat conductivity are included in the adhesive layer. The fillers are arranged in a longitudinal direction of the pressing roller. JP-2007-179009-A discloses a fixing member with an intermediate layer of a fluorine resin including carbon clusters such as fullerene and CNT. The intermediate layer is disposed between an elastic layer and a releasing layer.
However, in recent years, the demand for support of various types of recording media, in particular, support for thick papers has increased in the field of electrophotography. The above-described fixing members of JP-2010-066509-A, JP-2009-103882-A, and JP-2007-179009-A have a large difference in hardness between the elastic layer and the releasing layer or between the elastic layer and the intermediate layer. Thus, when a thick paper is employed, stress from deformation at an end portion of the thick paper concentrates at a bonding portion (i.e., interface) between the elastic layer and the releasing layer or the intermediate layer. As a result, plastic deformation of the releasing layer or the intermediate layer may occur, or the releasing layer or the intermediate layer may come off from the elastic layer.
JP-2010-152303-A discloses a fixing member including a surface elastic layer of porous fluorosilicone rubber with carbon fibers uniformly dispersed. JP-2011-237681-A discloses a foamed elastic layer including fluorosilicone rubber, and carbon fibers surface treated with a fluorine resin dispersed within the foamed elastic layer. However, when a releasing layer wears down, the carbon fibers may become exposed on the surface, resulting in a decline of releasing property.